Researchers at Oak Ridge National Laboratory are using neutron beams to shed light on the chemical mechanisms that influence soil carbon stability and its impact on future climate change. Sindhu Jagadamma, a post doc in ORNL’s Environmental Science Division and Climate Change Science Institute, is collaborating with the laboratory’s Neutron Sciences Division to conduct a novel study to understand the interaction of organic carbon with soil minerals at the nanometer scale.

Why is soil carbon stability important to climate modeling?

Jagadamma: Soil represents the largest active pool of carbon on land, but we’ve never had the most appropriate technology to investigate how it interacts with minerals. It’s mostly been viewed as a “black box.”

Because soil carbon is a significant component of the global carbon cycle, its stability is very important. We want to know how long carbon can be stored in the soil. The goal of our paper that was published in Geoderma this year was to determine how different carbon compounds become arranged on soil minerals and whether compounds are stacked on top of one another to increase carbon storage in soils. Once we understand this concept we’ll be able to better represent soil carbon dynamics in computer models.

Recently you and your Neutron Science colleagues, Haile Ambaye and Valeria Lauter, have used neutrons to study the architecture of organic carbon on minerals for the first time. Why is this study significant?

Jagadamma: Researchers have used other techniques like microscopy and spectroscopy to study soil carbon chemistry and pore structure, but the resolution and the sensitivity of those techniques are not fine enough to capture the layering of different carbon compounds on soil minerals. We used the intense neutron beam of ORNL’s Spallation Neutron Source to fill this gap by performing experiments on the Magnetism Reflectometer.

Neutrons are uncharged particles that can rapidly penetrate the electron clouds of atoms, allowing them direct interaction with the nucleus of light elements like carbon. By using neutron beams, we have confirmed that there are specific preferences in the layering of carbon compounds on minerals, bringing us one step closer to revealing the mystery of the “soil carbon black box.”

How will your research improve climate modeling?

Jagadamma: With the help of neutrons, we’ve learned that different carbon compounds can be arranged in a layered profile on minerals. We suppose that microbes degrade compounds at different rates depending on their position within the layered structural framework, but we don’t know that yet. We are planning to conduct further studies to determine whether this is true. Understanding controls on the stability of carbon could improve predictions of the rates of decomposition in climate models.

How did you get interested in this science?

Jagadamma: I was first exposed to the science of soils as an undergraduate in India. When I read more about this amazing natural resource, I was fascinated by the huge carbon reserve it contains. I began research in soil carbon cycling science at Ohio State University as a graduate student. During my graduate years, my research focused on the applied aspects of carbon cycling, meaning how we can modify the current farm management practices to increase the accumulation of carbon in soils. Here I developed a strong interest in learning the fundamental mechanisms that keep carbon in soil for such a long time.

My postdoctoral appointment at ORNL is giving me the opportunity to delve into the mechanistic understanding further, especially through the use of state-of-the-art neutron science. What really excites me is the realization that soil carbon is not a black box anymore. We now have the right techniques and skills to open this box and figure out what it contains.

Jagadamma is a co-author of 10 publications on soil carbon research. Her use of neutrons to study the soil-carbon interface is published in a paper titled “Neutron Reflectometry Reveals the Internal Structure of Organic Compounds Deposited on Aluminum Oxide” in Geoderma. Other ORNL co-authors of the paper are Melanie Mayes, Ambaye, Loukas Petridis, and Lauter.

The project was funded by the ORNL Laboratory Directed Research and Development program.